We propose to carry on studies in the following area: 1. Continue theoretical studies of spacial and density resolution and radiation dose, as well as the possible extension of CT scanning to three-dimensional imaging. 2. Continue studies on our bench top fan beam x-ray system-including analysis of the high pressure xenon chambers, electronics, digital to analog converters and computer algorithms. We propose an extensive program of study of phantoms to define the performance characteristics of the system. 3. Continue and expand the study of energy sensitive detection and Z scanning. We intend to pursue the study of alternating filter imaging to obtain simultaneous electron density and Z images. 4. Using the bench top system, we intend to pursue studies of the application of CT scanning to various problems in cancer diagnosis and therapy. This will include the possible applications of Z scanning for diagnosis and possible use of electron density images to obtain precise dose distributions for high energy radiation therapy.